1. Field of the Invention
This invention relates to a screen printer and its screen printing method. Particularly, this invention relates to the screen printer using a plurality of squeegees. This invention also relates to the screen printer using a pressure unit for pressing a screen.
2. Description of the Related Art
FIG. 12 illustrates a perspective view of the screen printer. FIG. 13 illustrates a schematic side view of the screen printer. FIG. 14 illustrates a schematic top view of the screen printer.
In FIG. 12, a screen printer 101, a base of the screen printer 102, a table 103 which is attached for allowing movement, a guide rail 104 for guiding the movement of the table, an operation box 105 of the screen printer, an operation switch 107 attached to the operation box, and a printing unit 109 for performing screen printing on a work placed on the table 103 are illustrated. In FIGS. 13 and 14, a work 110 placed on the table 103, a screen plate 200, a screen frame 1 of the screen plate 200, and a screen 201 affixed to the screen plate 200 are illustrated. A slider 106 for holding a squeegee 111 and a scraper (not illustrated) slides in directions of arrow A and arrow D, and a slide base 108 slides the slider 106.
The table 103 is attached for allowing left and right sliding along the guide rail 104 provided on the base 102. When the table 103 moves under the printing unit 109, the table 103 is stopped by a stopper (not illustrated), and the printing unit 109 performs screen printing on the work 110.
FIG. 15 illustrate an example of the screen plate 200.
The screen plate 200 for a combination screen is illustrated in FIG. 15.
In FIG. 15, the screen frame 1, a support screen 2, a print screen 3, and a joint part 4 of the support screen and the print screen are illustrated. The screen 201 includes the support screen 2, the print screen 3, and the joint part 4.
FIG. 16 illustrates a front surface of the print screen 3.
FIG. 17 illustrates a back surface of the print screen 3.
In FIGS. 16 and 17, a screen-mesh 30, and an emulsion 31 provided on a back of the screen-mesh 30 are illustrated. An opening 32 is provided in the emulsion 31. The opening 32 is provided for generating a print image. When an ink (paste) passes through the opening and sticks to the work 110, screen printing is performed on the work.
FIGS. 18 and 19 show cross-sectional views at Xxe2x80x94X part of the screen printer illustrated in FIG. 14. A squeegee holder 120 and a scraper holder 320 are attached to the slider 106 for allowing up and down movement by a mechanism which is not illustrated. In FIG. 18, the slider 106 is moving in the direction of arrow A, and the squeegee 111, secured for example, against squeegee bracket 111a, is pushed down in the direction of arrow B. Printing is performed on the work 110 by using an ink 51. The scraper holder 320 holds a scraper 311, and the scraper holder is moved up in a direction of arrow C during a printing operation by the squeegee. When printing is performed by using the squeegee 111, printing is performed with a high pressure. As illustrated in FIG. 18, the screen is pressed by a pressure applied to the squeegee at a point R in which the squeegee and the screen contact each other. When the squeegee moves, the point R moves on the surface of the screen.
In case of FIG. 19, the slider moves in a direction of arrow D. When the slider moves in the direction of arrow D, the squeegee holder 120 is pulled up in a direction of arrow E. At the same time, the scraper holder 320 is pushed down in a direction of arrow F, and the scraper 311 moves on the surface of the screen in contact with the screen 201. The scraper 311 has a function for pushing the ink 51, which has been moved to a right side of FIG. 19 by the squeegee 111, back to a left side of FIG. 19. The scraper 311 also has a function for re-coating the surface of the screen evenly with the ink after printing is performed by the squeegee 111.
The screen printer performs screen printing by moving the squeegee 111 in the direction of arrow A as illustrated in FIG. 18. As illustrated in FIG. 19, when the slider is moved in the direction of arrow D, the ink is returned, and the surface of the screen is evenly re-coated with the ink.
FIG. 20 illustrates a sectional view of the screen in case that the squeegee 111 in FIG. 18 has performed printing on the work 110. The ink 51 passes through the opening 32 of the emulsion provided on the back side of the screen-mesh, and sticks to the work 110. Since the squeegee 111 is made of an elastic material, e.g., urethane rubber, etc., when the squeegee 111 has passed, the ink 51 on the surface of the screen is evenly scraped.
In FIG. 21, the scraper 311 returns the ink. The scraper 311 is made of a metal, e.g., stainless, etc. The scraper includes a taper part 312 at an end, and contacts with the surface of the screen at point Q. Since the scraper 311 is made of the metal, e.g., stainless, etc., when the scraper 311 has passed, the surface of the screen is evenly coated with the ink 51. In this way, an evenly coated condition is generated. Therefore, next printing can be performed evenly by the squeegee 111.
FIG. 22 illustrates the printing unit 109 in a printing state. The screen 201 is evenly coated with the ink 51.
(a) of FIG. 22 illustrates a state before starting printing. In (b) of FIG. 22, a pressure P is applied to the squeegee 111, and printing is started. In (c) of FIG. 22, patterns 52, 53 and 54 have been printed on the work 110 from patterns which are generated on the screen 201 in advance. In (d) of FIG. 22 illustrates a time of completing printing is illustrated further including patterns 55 and 56. During printing in (b)-(d) of FIG. 22, the pressure P applied to the squeegee 111 is constant as shown in (e) of FIG. 22.
When printing is performed as illustrated in FIG. 22, a height H1 of the pattern 52 and a height H2 of the pattern 54 illustrated in (d) of FIG. 22 may differ. Even though the screen 201 is tightly stretched over the screen frame 1, angles vary in positions on the screen 201. Therefore, even if the constant pressure P is applied downward during printing, there is a possibility that a printed pattern may be spread forward in some printing position. Hence, such problems like uneven thickness of the ink on the work 110 and uneven printing have to be solved.
As shown in FIG. 22, angles xcex1, xcex2, and xcex3 between the screen 201 and the work 110 change during printing (xcex1 less than xcex2 less than xcex3). Since the angles between the screen 201 and the work 110 vary in printing positions, there are solving problems such as uneven thickness of the ink on the work 110 and uneven printing.
FIG. 23 illustrates a method for solving the above-stated uneven thickness of the ink.
In FIG. 23, during printing, the screen plate 200 is lifted up in a direction of arrow X by using a detaching apparatus (plate detaching apparatus) which is not illustrated. By detaching the screen plate 200 from a side in which printing is finished, changes in a tension in the positions on the screen 201 are intended to be ignored. Consequently, the height H1 of the pattern 52 and, for example, pattern 56 printed at an edge area of the work 110 and the height H2 of the pattern 54 printed at a center of the work 110 can become almost equal with the height patters 53 and 55 also being almost equal to edge patterns 52 and 56 and center pattern 54.
However, according to the method of lifting one side of the screen plate 200 as illustrated in FIG. 23, an excessive pressure is applied to the screen plate 200. As a result, printing patterns provided on the screen 201 might be shifted, and a durability of the screen plate 200 might be reduced.
FIG. 24 illustrates a screen printer with two squeegees according to the related art.
In (a) of FIG. 24, printing is performed by using the squeegee 111. In (b) of FIG. 24, printing is performed by using a squeegee 112.
The screen printer in FIG. 24 can print in both directions of arrows A and D. After printing is performed in (a) of FIG. 24, the work 110 is taken out, and another work 110 is put in. Then, printing is performed in (b) of FIG. 24. By repeating operations in (a) and (b) of FIGS. 24, printing can be performed in a higher speed.
FIG. 25 also illustrates screen printing by using two squeegees.
Squeegees 113 and 114 are arranged in a straight line. The screen printer as illustrated in FIG. 25 is used in case that an area between the squeegees 113 and 114 should not be printed or can not be printed due to roughness on the work.
FIGS. 24 and 25 illustrate the screen printer using two squeegees. However, as stated, no consideration is made for printing evenly on the work.
It is an object of a preferred embodiment of this invention to provide a screen printer for printing evenly on a work. Particularly, it is an object of a preferred embodiment of this invention to provide a screen printer for printing in higher quality by using a plurality of squeegees.
According to one aspect of this invention, a screen printer for performing screen printing on a work by using a squeegee includes a main squeegee for performing screen printing and a supplementary squeegee for supplementing screen printing by the main squeegee during screen printing by the main squeegee.
According to another aspect of this invention, a screen printer includes two squeegees, and the two squeegees are used together successively to print a determined area on a screen for one stroke.
According to another aspect of this invention, a screen printing method for a screen printer which has a main squeegee and a supplementary squeegee includes a step of performing screen printing by moving of the main squeegee in a printing direction with pressing a screen and a step of moving of the supplementary squeegee in the printing direction with pressing the screen by keeping a determined distance from the main squeegee in the printing direction during screen printing by the main squeegee.
According to another aspect of this invention, a screen printer for performing screen printing on a work by using a squeegee includes a main squeegee for performing screen printing and a pressure unit provided ahead in a printing direction during screen printing by the main squeegee for pressing a screen against the work.
According to another aspect of this invention, a screen printing method for a screen printer which has a main squeegee and a pressure unit includes a step of performing screen printing by moving the main squeegee in a printing direction with pressing a screen and a step of moving the pressure unit in the printing direction with pressing the screen by keeping a determined distance in the printing direction from the main squeegee during screen printing by the main squeegee.
According to another aspect of this invention, a screen printer for performing screen printing includes a first squeegee and a second squeegee for moving forward and backward. The first squeegee is a pressure squeegee for pressing the screen and the second squeegee is a main squeegee for performing screen printing in the forward movement, and the second squeegee is the pressure squeegee for pressing the screen and the first squeegee is the main squeegee for performing screen printing in the backward movement.
Further features and applications of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Other objects features, and advantages of the invention will be apparent from the following description when taken in conjunction with the accompany drawings.